Count Number of Nice Subarrays

Description

Given an array of integers nums and an integer k. A subarray is called nice if there are k odd numbers on it.

Return the number of nice sub-arrays.

 

Example 1:

Input: nums = [1,1,2,1,1], k = 3
Output: 2
Explanation: The only sub-arrays with 3 odd numbers are [1,1,2,1] and [1,2,1,1].

Example 2:

Input: nums = [2,4,6], k = 1
Output: 0
Explanation: There is no odd numbers in the array.

Example 3:

Input: nums = [2,2,2,1,2,2,1,2,2,2], k = 2
Output: 16

 

Constraints:

• 1 <= nums.length <= 50000
• 1 <= nums[i] <= 10^5
• 1 <= k <= nums.length

Solution(javascript)

/*
 * @lc app=leetcode id=1248 lang=javascript
 *
 * [1248] Count Number of Nice Subarrays
 */

// @lc code=start
/** Sliding Window 类型 992
 * @param {number[]} nums
 * @param {number} k
 * @return {number}
 */
const numberOfSubarrays = function (nums, k) {
  const atMost = (k) => {
    let left = 0
    let currentK = 0
    let count = 0
    for (let right = 0; right < nums.length; right++) {
      const num = nums[right]
      if (num % 2 === 1) {
        currentK += 1
      }
      while (currentK > k) {
        if (nums[left++] % 2 === 1) {
          currentK -= 1
        }
      }

      count += right - left + 1
    }
    return count
  }
  return atMost(k) - atMost(k - 1)
}
// @lc code=end